The present invention relates to a digital video recorder and, more particularly, to a method and apparatus for storing a compressed MPEG-2 transport data stream with a conventional digital video recorder.
A conventional digital video (DV) recorder records a digitized version of an analog television signal. The analog signal may be the signal of the NTSC (National Television Systems Committee) color television system of the United States and Japan, the PAL (Phase Alteration Line Rate) television system of parts of Europe, or the SECAM (Se'quentiel Couleur 'a Memoire) television system of France, Russia and eastern Europe. For example, to digitally record the analog television signal of the NTSC system, the separate luminance and chrominance signals of the video signal are first sampled and quantized. Intraframe compression is applied to the digital data representing the video signal using techniques such as adaptive quantization (AQ), discrete cosine transformation (DCT), and variable length coding (VLC). Following compression, error correction is added to the data. The audio portion of the signal is processed in a similar manner. The digital audio and video data are copied to data elements of a digital video (DV) frame data structure and the audio and video data elements of the DV frame structure are stored as separate segments of recording tracks on a magnetic tape.
The input and output of most DV recorders are by means of isochronous data transport as defined by the IEEE 1394-1995, STANDARD FOR A HIGH PERFORMANCE SERIAL BUS, incorporated herein by reference. The IEEE 1394 standard defines a basic mechanism for real time data transport including an isochronous data packet 10, as illustrated in FIG. 1. However, the IEEE 1394 standard does not establish the protocols needed for specific application requirements such as sending DV data over the bus. The format of the data structure for isochronous transmission of DV data across the IEEE 1394 serial bus is described in the International Standards Organization (ISO)/International Electrotechnical Commission (IEC) standards for DIGITAL INTERFACE FOR CONSUMER ELECTRONIC AUDIO/VIDEO EQUIPMENT, ISO/IEC 61883-1 and 61883-2, incorporated herein by reference. ISO/IEC 61883 defines the Common Isochronous Packet (CIP) format that is the basis of the 1394 DV data packet 30, illustrated in FIG. 2. The DV packet 30 comprises a CIP header 32 and a data field 34 of 480 bytes. For isochronous transmission on the IEEE 1394 bus, the DV data packet 30 is inserted into the data block of the IEEE 1394 isochronous data packet 10.
The IEEE 1394 bus sequences through three general phases: a cycle initiation phase, an isochronous phase, and an asynchronous phase. At the completion of the cycle initiation phase, transfer of isochronous data packets 10 is enabled. Devices connected to the bus having an allocated isochronous channel arbitrate for the bus. When a device gains access to the bus, it locates the start of the DV video frame and buffers the next 250 valid data packets to collect a complete DV frame. The CIP headers are discarded and the remaining 120,000 bytes defines an NTSC DV frame.
A 525 lines, NTSC DV video frame 50 comprises odd and even video fields and is encoded into ten digital interface format (DIF) sequences 52, as illustrated in FIG. 3. Each DIF sequence 54 comprises 150 DIF blocks 54 as illustrated in FIGS. 3 and 4. The 150 DIF blocks comprise a header (H) section 70, a subcode (SC) section 72, a video auxiliary (VAUX) section 74, and an audio and video data section 75. The audio data section 76 (indicated by a bracket in FIG. 4) comprises nine (A0-A8) audio DIF blocks. The video portion of the audio-video section 75 comprises 135 (V0-V134) video DIF blocks 78 (indicated by a bracket in FIG. 4). Referring to FIG. 3 each DIF block 54 includes an ID section 56 and a data section 58.
Digital recording of analog television signals provides a number of advantages over analog recording of those signals. However, television is in transition from an analog system to a digital system based on the MPEG-2 video compression standard. In the digital television (DTV) system, signals for each of the elements of a television program are digitized. The digital elementary data streams are compressed and then multiplexed into a single MPEG-2 transport data stream for transmission to a receiver. At the receiver, the transport stream is separated into the constituent elementary data streams which are decompressed and presented to the viewer. MPEG-2 transport data streams can be recorded with a dedicated MPEG video recorder. However, purchasing a dedicated video recorder to record MPEG video, particularly during the transition to DTV, is an undesirable additional expense.
What is desired, therefore, is a method of storing an MPEG transport data stream on a conventional DV format video recorder for playback on a DTV receiver.